Massive Binary Stars Found Cuddling Together in Stellar Nursery

Astronomers from the University of Leeds have discovered the closest-orbiting pair of massive stars in a binary system ever seen, huddling together in the stellar nursery in which they were born. This discovery could help researchers test theories on the formation of high-mass binary stars throughout the galaxy.

One of the stars, known as PDS 27, orbits just 30 astronomical units (or AU’s, the average distance between the Earth and Sun), away from its stellar partner. This is 4.5 billion kilometers (2.8 billion miles) or, roughly, the distance between our Sun and the planet Neptune.

“This is a very exciting discovery, observing and simulating massive binaries at the early stages of their formation is one of the main struggles of modern astronomy. With PDS 27 and its companion we have now found the closest, most massive young stellar objects in binaries resolved to date,” said Evgenia Koumpia of the School of Physics and Astronomy at the University of Leeds.

Astronomers are still uncertain exactly how binary stars develop, but this artist’s impression shows such a system as it form from a massive, swirling cloud of gas and dust. Image credit: B. Saxton, NRAO/AUI/NSF

Binary star systems are those in which two stars orbit around a common center of mass. Although astronomers have known for several years that PDS 27 is a young, massive star, it is only now that researchers have found it exists in a binary system. Roughly one-third of the stars in the Milky Way Galaxy reside in systems with two or more stars. The nearest star system to our own Sun, Alpha Centauri, is a binary system locked in a gravitational embrace with a third star, Proxima Centauri.

The star PDS 27 is roughly 10 times more massive than our own sun, and the system resides 8000 light years from Earth.

The binary star system PDS 27 was thought to be a single star, due to the small separation between each body in the system. Image credit: Evgenia Koumpia, University of Leeds

Researchers at Leeds also discovered a second, previously known, binary system, once thought to be a single star dubbed PDS 37. That pair is separated by between 42 and 54 astronomical units, approximately the spacing between the Sun and Pluto. Although this pair is not as close as the the system containing PDS 27, the discovery still serves a vital service for astronomers worldwide.

“There is a shortage of known young massive binary systems in charted space. High mass stars have comparatively short lifespans, burning out and exploding as supernovae in only a few million years, making them difficult to spot. This limits our ability to test the theories on how these stars form,” Koumpia explains.

The PIONIER instrument, part of the Very Large Telescope Interferometer (VLTI) at the Paranel Observatory, was utilized to separate images of the stars for the first time. This instrument, operated by the European Southern Observatory (ESO), combines images from four telescopes, each 8.2 meters (27 feet) in diameter, into a single picture, simulating the performance of a single telescope 130 meters (427 feet) across. Each pair of telescopes constitutes a baseline, the length of which is determined by the distance between each telescope.

“The greater the number of baselines, the more information you get on the morphology of your image, e.g., the level of detail for the objects,” said Julien Milli, astronomer at ESO.

By moving the four telescopes of the Paranel Observatory along sets of rails, it is possible to see objects in detail far greater than any single telescope could accomplish. Image credit: G.Hüdepohl (atacamaphoto.com)/ESO

Nearly all massive stars are found with one or more partners, but why this is the case remains a mystery to astronomers. What is known is that being in a system containing two or more stars has a significant effect on the evolution and development of these stellar bodies. Now, these new discoveries may help astronomers find the answer to questions about how these systems are born, live out their lives, and perish.